Today’s
commercial explosives have resulted from a gradual evolution that began over
600 years ago. Black powder was first used in guns around the 14th
centaury. But it was not until the 17th Centaury that this explosive
began to replace fire setting as the principle method for loosening rock. As
black powder became accepted in the mining Industry, the number of accidents
increased and a need for safe explosives and initiating systems emerged. N G Nair & Mr. M C Sharma At MalanjkhandCopper Project.IN- HOLE DELAY SYSTEM, CHARGING & POSITIONING PRIMER

Explosives
have been the primary method of breaking and loosening rock since the
introduction of black powder and largely through dedication to research and
development in safety and quality, have evolved into today’s wide range of safe
and cost-effective products. When
properly initiated, commercial explosive are rapidly converted into gases at
high temperature and pressure. When confined by rock, expanding explosion gases
result in extremely high strains in the rock. The energy released during
detonation acts equally in all directions but as one would expect, tends to
escape through any path(s) of least resistance. Therefore, blast holes should
to charged and stemmed so that the gases are confined for sufficient time toprovide optimum breakage, displacement and looseness of the blasted rock. An
explosive contains the following ingredients: An
oxidizer is a chemical which provides oxygen for the reasons. Ammonium nitrate
is b far the most common oxidiaser. Fuel
reacts with oxygen to provide heat. Common fuels include fuel oil and aluminums
powder. A
sensiiser provides voids which acts as hot spots and at which reaction starts
during detonation. Semsitisers are generally air or gas in the form of very
small bubbles, sometimes encapsulated in glass micro balloons (GNBs). In-hole
delay systems provide a predetermined time interval between each down line
initiation and detonation of the corresponding explosive charge. A suitable
time delay ensues that the initiation signal has reached the detonators within
each charge before it or adjacent charges begin to disrupt the surrounding rock
mass. This minimizes the risk of downlines being physically damaged or cut off
by ground moment during the balst, and permits the use of longer inter-row
delays where required for improved blast performance. In
general it is recommended that all blast holes should contain two or more
primers. This multipoint initiation provides security against disruption of the
explosive column by round moment, of propagation failure within the charge because
of water penetration, etc. Whether the primary delay in the charge is number N
eg 600 ms the insurance delay will be number N1 ie. 650 ms to provide single
point initiation under normal circumstances. Charging
and Measuring Blast holes.All
blast holes should be cleaned immediately after the drilling to ensure they are
clear and are drilled to the correct depth. This is particularly important in
broken and joined ground which falls in easily. Blast holes should be plugged
immediately after drilling to prevent water, rocks and drill cuttings from
entering the hole. Drill cuttings and rock may need to be cleared from around
the collar to prevent these from falling into the blast hole during charging. All
blstholes must have their depth measured and recorded immediately before
charging. Short blastholes can lead to over charging toe, and digging problems,
while overcharged blast holes cause fly rock hazards, noise, and reduce the
effectiveness of the explosives.

N G Nair & Mr. M C Sharma at Malanjkhand Copper Project.

Blast
holes which are too deep must to back filled to the correct depth to prevent
excessive vibration and damage drilled are also caused by excessive blast hole
depth on upper benches. Bore hole charging, any blocked blast holes should be
cleared with a charging pole or steel bar. It may be necessary to bring a drill
back to the blast to clear, or re-drill some blast holes. A torch or mirror is
often useful to examine the blast hole for blockages, cavity or rough sections
before charging. Blasting in Mines - Video Clips. Blast Hole Open Stopes ,

Controlled blasting in an open-pit mine for improved slope stability.A controlled blasting programme (presplitting) was adopted in an open-pit copper mine in order to improve the stability of the resulting cut slopes. The aim was to reduce over break and minimize damage to the final pit walls from production blasts. The use of presplitting allowed considerably higher benches to be adopted with much steeper overall slope angles.